( 10 ) 
The cloaca is a pocket, in which ihc rectum, the ureters, and 
the spermatic canals, or, in the female, the oviductuses, (i) termi- 
nate ; its exterior opening is the anus. (2) In general. Birds do 
not discharge their urine, but it mixes with the soHd excrements. 
The Ostriches, alone, have the cloaca sufficiently dilated for the 
urine to accumulate there. 
In the greater number of genera, copulation takes place by the 
juxta- position of the anus; the Ostriches and several Palmipedes, 
however, have a penis, with a deep furrow on the outer surface, 
by which the seed is conducted. The testicles are situated in the 
interior-, above the kidnies, and near the lungs ; there is but one 
ovary and one oviductus. 
The egg detached from the ovary, where the yolk only is per-- 
ceptible, imbibes the exterior hquor, called the ivliiie, in the 
upper part of the oviductus, and is furnished with its shell in the 
lower part of the canal ; the young one is developed by incubation, 
unless the heat of the climate is sufficient, as it is with Ostriches. 
It has a horny tip at the end of its beak, which enables it to cleave 
the egg, and which falls off a few days after birth. (3) 
three stomachs, since it feeds almost entirely on grain, which is one of 
the most difficidt aliments to digest. 
(1) In the winter season the oviductuses of Birds are scarcely distin- 
guisliable, on dissection ; but in the spring they are very evidently 
developed, and the end nearest the opary enlarges considerably, and 
environs it, to receive the falling eggs. 
(2) In Mammalia^ the rectum is continued to the anus, the ureters 
pass from the kidnies into the bladder, and both these channels and 
apertures are distinct ; in Birds the anus is the inferior opening of a 
large bag, called cloaca, from its being a reservoir for the faeces as well 
as the secretions, and into which the rectum., the ureters^ the spermatic 
ducts, and the bursa fabric ii discharge their contents. The use of the 
secretion discharged into the cloaca by the bursa fabricii, which does 
not exist in Mammalia, Is considered by some Naturahsts to be that of 
colouring the yolk of the egg. 
(3) Eggs require a heat of nearly 54*^ of Farenheit to enable the 
germ to develope itself. Almost all Birds sit and fast during the incu- 
bation : they feel a sort of fever produced by maternal love, which 
sometimes elevates their temperature as high as 79^. "We first observe 
the germ besprinkled with red spots (which we soon recognise to be 
blood vessels) towards the centre, where we next perceive the heart in 
motion ; we afterwards begin to distinguish the head, with two large 
eyes; the beak, the wings, and the claws are then developed; but all 
these parts are in a state of considerable softness. The albuminous 
matter is absorbed in proportion to the developement of the foetus. 
The yolk does not appear to diminish in size, and it is only at the mo- 
